Re: [PATCH v8 27/40] x86/boot: Add Confidential Computing type to setup_data

From: Brijesh Singh <brijesh.singh@amd.com>
To: Dave Hansen <dave.hansen@intel.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org,
	kvm@vger.kernel.org, linux-efi@vger.kernel.org,
	platform-driver-x86@vger.kernel.org, linux-coco@lists.linux.dev,
	linux-mm@kvack.org
Cc: brijesh.singh@amd.com, Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, Joerg Roedel <jroedel@suse.de>,
	Tom Lendacky <thomas.lendacky@amd.com>,
	"H. Peter Anvin" <hpa@zytor.com>,
	Ard Biesheuvel <ardb@kernel.org>,
	Paolo Bonzini <pbonzini@redhat.com>,
	Sean Christopherson <seanjc@google.com>,
	Vitaly Kuznetsov <vkuznets@redhat.com>,
	Jim Mattson <jmattson@google.com>,
	Andy Lutomirski <luto@kernel.org>,
	Dave Hansen <dave.hansen@linux.intel.com>,
	Sergio Lopez <slp@redhat.com>, Peter Gonda <pgonda@google.com>,
	Peter Zijlstra <peterz@infradead.org>,
	Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>,
	David Rientjes <rientjes@google.com>,
	Dov Murik <dovmurik@linux.ibm.com>,
	Tobin Feldman-Fitzthum <tobin@ibm.com>,
	Borislav Petkov <bp@alien8.de>,
	Michael Roth <michael.roth@amd.com>,
	Vlastimil Babka <vbabka@suse.cz>,
	"Kirill A . Shutemov" <kirill@shutemov.name>,
	Andi Kleen <ak@linux.intel.com>,
	"Dr . David Alan Gilbert" <dgilbert@redhat.com>,
	tony.luck@intel.com, marcorr@google.com,
	sathyanarayanan.kuppuswamy@linux.intel.com
Subject: Re: [PATCH v8 27/40] x86/boot: Add Confidential Computing type to setup_data
Date: Mon, 13 Dec 2021 08:49:41 -0600	[thread overview]
Message-ID: <f442ca7f-4530-1443-27eb-206d6ca0e7a4@amd.com> (raw)
In-Reply-To: <2a5cfbd0-865c-2a8b-b70b-f8f64aba5575@intel.com>

On 12/10/21 2:30 PM, Dave Hansen wrote:
> On 12/10/21 12:18 PM, Brijesh Singh wrote:
>> On 12/10/21 1:12 PM, Dave Hansen wrote:
>>> On 12/10/21 7:43 AM, Brijesh Singh wrote:
>>>> +/* AMD SEV Confidential computing blob structure */
>>>> +#define CC_BLOB_SEV_HDR_MAGIC	0x45444d41
>>>> +struct cc_blob_sev_info {
>>>> +	u32 magic;
>>>> +	u16 version;
>>>> +	u16 reserved;
>>>> +	u64 secrets_phys;
>>>> +	u32 secrets_len;
>>>> +	u64 cpuid_phys;
>>>> +	u32 cpuid_len;
>>>> +};
>>> This is an ABI structure rather than some purely kernel construct, right?
>>
>> This is ABI between the guest BIOS and Guest OS. It is defined in the OVMF.
>>
>> https://nam11.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgithub.com%2Ftianocore%2Fedk2%2Fblob%2Fmaster%2FOvmfPkg%2FInclude%2FGuid%2FConfidentialComputingSevSnpBlob.h&amp;data=04%7C01%7Cbrijesh.singh%40amd.com%7C460f6abff7f04e065c9108d9bc1bfcf7%7C3dd8961fe4884e608e11a82d994e183d%7C0%7C0%7C637747650681544593%7CUnknown%7CTWFpbGZsb3d8eyJWIjoiMC4wLjAwMDAiLCJQIjoiV2luMzIiLCJBTiI6Ik1haWwiLCJXVCI6Mn0%3D%7C3000&amp;sdata=GI1fAngRJ%2Bj4hcM91UutVXlS1F7kfk2xxtG6I%2BL%2FRYc%3D&amp;reserved=0
>>
>> SEV-SNP FW spec does not have it documented; it's up to the guest BIOS
>> on how it wants to communicate the Secrets and CPUID page location to
>> guest OS.
> 
> Well, no matter where it is defined, could we please make it a bit
> easier for folks to find it in the future?
> 

Noted, I will add a comment so that readers can find it easily. 
Additionally, I will create a doc and get it published on 
developer.amd.com/sev so that information is documented outside the 
source code files.

>>> I searched through all of the specs to which you linked in the cover
>>> letter.  I looked for "blob", "guid", the magic and part of the GUID
>>> itself trying to find where this is defined to see if the struct is correct.
>>>
>>> I couldn't find anything.
>>>
>>> Where is the spec for this blob?  How large is it?  Did you mean to
>>> leave a 4-byte hole after secrets_len and before cpuid_phys?
>> Yes, the length is never going to be > 4GB.
> 
> I was more concerned that this structure could change sizes if it were
> compiled on 32-bit versus 64-bit code.  For kernel ABIs, we try not to
> do that.
> 
> Is this somehow OK when talking to firmware?  Or can a 32-bit OS and
> 64-bit firmware never interact?
> 

For SNP, both the firmware and OS need to be 64-bit. IIRC, both the 
Linux and OVMF do not enable the memory encryption for the 32-bit.

thanks